1. Field of the Invention
The invention relates to bottle stoppers and more particularly to synthetic stoppers for use in wine bottles and other similarly packaged products.
2. Description of Related Art
Natural cork is the most common material for making stopper-type bottle closures. The use of cork to finish wine and other food products dates back centuries. Natural cork is a wood product. The disadvantages of the use the natural wood product are well-known. These disadvantages include, inconsistency in structure leading to leakage and premature aging of the bottle contents, susceptibility of the contents to contamination from trichloroanisole (TCA) which gives the bottle contents a musty aroma, and a tendency to dry and crumble with age, storage, or dry environments.
Alternatives to natural cork stoppers have been known for many years. U.S. Pat. No. 466,169 issued to Hume discloses a stopper formed of a strip of textile material, such as canvas, filled with rubber and rolled up in the shape of a tapered stopper The resulting stopper structure consists of a core of textile material surrounded and enveloped with rubber. U.S. Pat. No. 512,705 issued to Holmes discloses a method of making a cork-like stopper of fiber pulp by pressing the pulp into proper form in suitable molds. The stopper can be used directly from the mold. However, in order to render the stopper water and acid proof, the stopper is dipped in melted paraffin wax.
Synthetic closures have also been developed to remedy the disadvantages associated with natural wood bark cork. For example, U.S. Pat. No. 281,333 issued to Barrett discloses a method of making a stopper consisting of pressing or forcing suitable plastic material, such as lignite, into a tube in a mold of vulcanite, xylonite, celluloid, or like material. The molded stopper produced is of a plastic material with a skin of vulcanite, xylonite, celluloid, or like material. U.S. Pat. No. 5,480,915 issued to Burns discloses the use of a thermoplastic elastomer and a commercially available blowing agent injection molded to form a porous cork-like structure. U.S. Pat. No. 4,188,457 issued to Throp discloses the use of a foam plastic injection-molded closure made with an ethylene vinyl acetate (EVA) polymer formed with sodium metabisulphite. French Patent No. 1,518,450 issued to Daicel Ltd. describes a closure produced by compressing a mat of thermoplastic fibers to form a porous plug. U.S. Pat. No. 4,042,543 issued to Strickman, et al., describes a stopper that combines a polymer with cork particles. European Patent Application 92100058.4 filed by Fantin on Jan. 9, 1991, and published Jul. 29, 1992, describes a plastic stopper with a cylindrical elastic insert made of granulated cork or a high density plastic material with resilient characteristics, or natural or synthetic rubber.
The difficulty with these prior art structures are numerous. First, the synthetic stoppers are not compatible with conventional cork insertion machinery. A standard wine bottle throat or neck has an inside diameter of approximately 18.5 mm .+-.0.5 mm. Thus, a stopper must have a slightly larger diameter to properly seal the bottle. Cork insertion machinery is used to compress the stopper and insert the stopper into the neck of the bottle. Upon compression in the cork insertion machinery, the cork's diameter is reduced to approximately 15.0 mm diameter. The prior art stoppers cannot withstand the compression of the corking equipment without cutting, creasing, or wrinkling. This is particularly true with those stoppers whose inner density or elasticity is less than their outer density or elasticity. In such cases, the compression machinery overcomes the resistance of the outer walls of the stopper, causing the stopper to cut, crease, or wrinkle. A cut, creased, or wrinkled stopper will not completely expand to its desired shape in the bottle and thus will not properly seal the bottle. U.S. Pat. No. 4,091,136, issued to O'Brien, et al., seeks to remedy the problem of creasing or wrinkling by abrading or cutting off the outer, more dense, layer of its extruded polymer foam stopper, then coating the remaining polymer foam with a wax. This necessitates extra process steps and creates a great deal of wasted material and dust particles.
Other difficulties associated with prior art stoppers include a difficulty in extraction of the stopper from the bottle due to poor closure compressibility; poor compressive and sealing properties; and the possibility of extraction of undesirable taste and aromas from plasticizers and other additives or from a chemical reaction between the stopper and the wine. Finally, a significant obstacle to the use of the thermoplastic stoppers is the relatively high cost associated with producing thermoplastic stoppers by a conventional injection molding process.